Any meticulous gardener who has cast a critical eye on a neighbor's less well-tended patch can understand the urge to make orderly and set right that which is not. Over the past decade Norway, one of the world's most prosperous and tranquil nations, has forged a reputation as a skillful international mediator, able to eke out peace agreements where weightier foreign-policy players had failed. From Latin America to Southeast Asia, Norway has brought its diplomatic talents to bear. Even now, with its defining achievement  the 1993 Israeli-Palestinian Oslo peace accord  in ruins, Norway perseveres, determined to bring order to...